Russian dandelion [Taraxacum kok-saghyz (TKS)] is a promising alternative to the Para rubber tree (Hevea brasiliensis) as a source of natural rubber; however, rubber yields must be improved for this undomesticated species to become a profitable new crop. Half-sib family recurrent selection was conducted for four cycles to increase rubber yield, estimated as the product of rubber percentage, and root dry weight per plant. Two distinct populations were developed for adaptation to sand and loam soil types. Rubber percentage increased from 4.17% for the cycle 0 (C0) population to 6.40% for the C4-loam population. Rubber yield also increased from 0.15 to 0.22 g/plant after four selection cycles. Although phenotypic variation was observed, selection had no effect on root weight; all populations averaged 3.70 g/plant. Rubber yield and percentage and root dry weight were not increased after four selection cycles on sandy soils, likely because of poor adaptation and high environmental variation. Year and soil type affected rubber yields; however, rubber percentage was more stable than root dry weight. Overall, russian dandelion can be improved for rubber yield, and further studies with increased error control should be considered to enhance root dry weight.
Russian dandelion [Taraxacum kok-saghyz (TKS)] is a promising candidate for introducing natural rubber production into North America. Seeds normally germinate in a humid microenvironment, such as the thatch layer of a lawn or under a canopy of grass; however, 5% to 15% establishment is often observed on bare soil, presumably due to water stress. Phenotypic selection and half-sib family recurrent selection were conducted for three cycles to improve germination in vitro, under low osmotic potential (Ψs), using a polyethylene glycol (PEG) solution. Populations were then tested for establishment on bare soil in the greenhouse and field. Germination under water stress in vitro increased from 5.8% for the cycle 0 (C0) population to 40.8% and 47.8% for the C3-phenotypic and C3-half-sib family populations, respectively. Soil establishment in the greenhouse and field was improved up to two- and 4-fold, respectively, compared with the C0, in two of four greenhouse experiments and three of eight field experiments. Overall, recurrent selection for germination under water stress in vitro has potential to improve establishment in the field and can be incorporated into current breeding programs to support the overall goal of creating cultivars with high-rubber yield.